The xylanase activity of the new thermophilic, anaerobic, Clostridium sp. EPP100 was induced by xylan, cellobiose, and lactose, a pattern previously noted only in cellulolytic organisms. The lactose-induced xylanase had microcrystalline cellulose binding activity. induction of xylanase activity was dependent on inducer concentration and was not fully repressible by glucose, xylose, or any mono-sugars tested. The beta-glycosidases and xylanase were not induced coordinately by lactose and cellobiose.